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                    2.1：计数器示例
            
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                    2.4：资源管理
            
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                    2.5：调试Flutter APP
            
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                    第三章：基础组件
            
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                    3.1：Widget简介
            
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                    3.2：状态管理
            
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                    3.3：文本、字体样式
            
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                    3.4：按钮
            
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                    3.6：单选框和复选框
            
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                    3.7：输入框和表单
            
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                    第四章：布局类组件
            
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                    4.1：布局类组件简介
            
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                    4.2：线性布局（Row、Column）
            
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                    4.3：弹性布局（Flex）
            
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                    4.4：流式布局（Wrap、Flow）
            
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                    4.5：层叠布局（Stack、Positioned）
            
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                    第五章：容器类组件
            
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                    5.1：填充（Padding）
            
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                    5.2：尺寸限制类容器（ConstrainedBox等）
            
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                    5.3：装饰容器（DecoratedBox）
            
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                    5.4：变换（Transform）
            
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                    5.5：Container容器
            
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                    5.6：Scaffold、TabBar、底部导航
            
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                    5.7：剪裁（Clip）
            
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                    第六章：可滚动组件
            
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                    6.1：可滚动组件简介
            
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                    6.2：SingleChildScrollView
            
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                    6.3：ListView
            
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                    6.4：GridView
            
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                    6.5：CustomScrollView
            
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                    6.6：滚动监听及控制（ScrollController）
            
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                    第七章：功能型组件
            
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                    7.1：导航返回拦截（WillPopScope）
            
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                    7.2：数据共享（InheritedWidget）
            
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                    7.3： 跨组件状态共享（Provider）
            
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                    7.4：颜色和主题（Theme）
            
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                    7.5：异步UI更新（FutureBuilder、StreamBuilder）
            
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                    7.6：对话框详解
            
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        <li class="header">进阶篇</li>
        
        
    
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                    第八章：事件处理与通知
            
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        <li class="chapter " data-level="3.1.1" data-path="../chapter8/listener.html">
            
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                    8.1：原始指针事件处理
            
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        <li class="chapter " data-level="3.1.2" data-path="../chapter8/gesture.html">
            
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                    8.2：手势识别
            
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        <li class="chapter " data-level="3.1.3" data-path="../chapter8/eventbus.html">
            
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                    8.3：全局事件总线
            
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                    8.4：通知(Notification)
            
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        <li class="chapter " data-level="3.2" data-path="../chapter9/">
            
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                    第九章：动画
            
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        <li class="chapter " data-level="3.2.1" data-path="../chapter9/intro.html">
            
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                    9.1：Flutter动画简介
            
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                    9.2：动画结构
            
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                    9.3：自定义路由过渡动画
            
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                    9.4：Hero动画
            
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                    9.5：交织动画
            
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                    9.6：通用“动画切换”组件（AnimatedSwitcher）
            
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                    9.7：动画过渡组件
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.3" data-path="../chapter10/">
            
                <a href="../chapter10/">
            
                    
                    第十章：自定义组件
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.3.1" data-path="../chapter10/intro.html">
            
                <a href="../chapter10/intro.html">
            
                    
                    10.1：自定义组件方法简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.3.2" data-path="../chapter10/combine.html">
            
                <a href="../chapter10/combine.html">
            
                    
                    10.2：组合现有组件
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.3.3" data-path="../chapter10/turn_box.html">
            
                <a href="../chapter10/turn_box.html">
            
                    
                    10.3：组合实例：TurnBox
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.3.4" data-path="../chapter10/custom_paint.html">
            
                <a href="../chapter10/custom_paint.html">
            
                    
                    10.4：自绘组件（CustomPaint与Canvas）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.3.5" data-path="../chapter10/gradient_circular_progress_demo.html">
            
                <a href="../chapter10/gradient_circular_progress_demo.html">
            
                    
                    10.5：自绘实例：圆形渐变进度条(自绘)
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.4" data-path="../chapter11/">
            
                <a href="../chapter11/">
            
                    
                    第十一章：文件操作与网络请求
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.4.1" data-path="../chapter11/file_operation.html">
            
                <a href="../chapter11/file_operation.html">
            
                    
                    11.1：文件操作
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.2" data-path="../chapter11/http.html">
            
                <a href="../chapter11/http.html">
            
                    
                    11.2：Http请求-HttpClient
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.3" data-path="../chapter11/dio.html">
            
                <a href="../chapter11/dio.html">
            
                    
                    11.3：Http请求-Dio package
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.4" data-path="../chapter11/download_with_chunks.html">
            
                <a href="../chapter11/download_with_chunks.html">
            
                    
                    11.4：实例：Http分块下载
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.5" data-path="../chapter11/websocket.html">
            
                <a href="../chapter11/websocket.html">
            
                    
                    11.5：WebSocket
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.6" data-path="../chapter11/socket.html">
            
                <a href="../chapter11/socket.html">
            
                    
                    11.6：使用Socket API
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.7" data-path="../chapter11/json_model.html">
            
                <a href="../chapter11/json_model.html">
            
                    
                    11.7：Json转Dart Model类
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.5" data-path="../chapter12/">
            
                <a href="../chapter12/">
            
                    
                    第十二章：包与插件
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.5.1" data-path="../chapter12/develop_package.html">
            
                <a href="../chapter12/develop_package.html">
            
                    
                    12.1：开发package
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.2" data-path="../chapter12/platform-channel.html">
            
                <a href="../chapter12/platform-channel.html">
            
                    
                    12.2：平台通道简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.3" data-path="../chapter12/develop_plugin.html">
            
                <a href="../chapter12/develop_plugin.html">
            
                    
                    12.3：开发Flutter插件
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.4" data-path="../chapter12/android_implement.html">
            
                <a href="../chapter12/android_implement.html">
            
                    
                    12.4：插件开发：实现Android端API
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.5" data-path="../chapter12/ios_implement.html">
            
                <a href="../chapter12/ios_implement.html">
            
                    
                    12.5：插件开发：实现IOS端API
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.6" data-path="../chapter12/texture_platformview.html">
            
                <a href="../chapter12/texture_platformview.html">
            
                    
                    12.6：Texture和PlatformView
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.6" data-path="../chapter13/">
            
                <a href="../chapter13/">
            
                    
                    第十三章：国际化
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.6.1" data-path="../chapter13/multi_languages_support.html">
            
                <a href="../chapter13/multi_languages_support.html">
            
                    
                    13.1：让App支持多语言
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.6.2" data-path="../chapter13/locallization_implement.html">
            
                <a href="../chapter13/locallization_implement.html">
            
                    
                    13.2：实现Localizations
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.6.3" data-path="../chapter13/intl.html">
            
                <a href="../chapter13/intl.html">
            
                    
                    13.3：使用Intl包
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.6.4" data-path="../chapter13/faq.html">
            
                <a href="../chapter13/faq.html">
            
                    
                    13.4：国际化常见问题
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.7" data-path="./">
            
                <a href="./">
            
                    
                    第十四章：Flutter核心原理
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.7.1" data-path="flutter_ui_system.html">
            
                <a href="flutter_ui_system.html">
            
                    
                    14.1：Flutter UI系统
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.7.2" data-path="element_buildcontext.html">
            
                <a href="element_buildcontext.html">
            
                    
                    14.2：Element和BuildContext
            
                </a>
            

            
        </li>
    
        <li class="chapter active" data-level="3.7.3" data-path="render_object.html">
            
                <a href="render_object.html">
            
                    
                    14.3：RenderObject与RenderBox
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.7.4" data-path="flutter_app_startup.html">
            
                <a href="flutter_app_startup.html">
            
                    
                    14.4：Flutter从启动到显示
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.7.5" data-path="image_and_cache.html">
            
                <a href="image_and_cache.html">
            
                    
                    14.5：Flutter图片加载与缓存
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    

    
        
        <li class="header">实例篇</li>
        
        
    
        <li class="chapter " data-level="4.1" data-path="../chapter15/intro.html">
            
                <a href="../chapter15/intro.html">
            
                    
                    第十五章：一个完整的Flutter应用
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="4.1.1" data-path="../chapter15/intro.html">
            
                <a href="../chapter15/intro.html">
            
                    
                    15.1：应用简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.2" data-path="../chapter15/code_structure.html">
            
                <a href="../chapter15/code_structure.html">
            
                    
                    15.2：APP代码结构
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.3" data-path="../chapter15/models.html">
            
                <a href="../chapter15/models.html">
            
                    
                    15.3：Model类定义
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.4" data-path="../chapter15/globals.html">
            
                <a href="../chapter15/globals.html">
            
                    
                    15.4：全局变量及共享状态
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.5" data-path="../chapter15/network.html">
            
                <a href="../chapter15/network.html">
            
                    
                    15.5：网络请求封装
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.6" data-path="../chapter15/entry.html">
            
                <a href="../chapter15/entry.html">
            
                    
                    15.6：App入口及首页
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.7" data-path="../chapter15/login_page.html">
            
                <a href="../chapter15/login_page.html">
            
                    
                    15.7：登录页
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.8" data-path="../chapter15/language_and_theme_setting.html">
            
                <a href="../chapter15/language_and_theme_setting.html">
            
                    
                    15.8：多语言和多主题
            
                </a>
            

            
        </li>
    

            </ul>
            
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                                <h1 id="143-renderobject&#x548C;renderbox">14.3 RenderObject&#x548C;RenderBox</h1>
<p>&#x5728;&#x4E0A;&#x4E00;&#x8282;&#x6211;&#x4EEC;&#x8BF4;&#x8FC7;&#x6BCF;&#x4E2A;<code>Element</code>&#x90FD;&#x5BF9;&#x5E94;&#x4E00;&#x4E2A;<code>RenderObject</code>&#xFF0C;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x901A;&#x8FC7;<code>Element.renderObject</code> &#x6765;&#x83B7;&#x53D6;&#x3002;&#x5E76;&#x4E14;&#x6211;&#x4EEC;&#x4E5F;&#x8BF4;&#x8FC7;<code>RenderObject</code>&#x7684;&#x4E3B;&#x8981;&#x804C;&#x8D23;&#x662F;Layout&#x548C;&#x7ED8;&#x5236;&#xFF0C;&#x6240;&#x6709;&#x7684;<code>RenderObject</code>&#x4F1A;&#x7EC4;&#x6210;&#x4E00;&#x68F5;&#x6E32;&#x67D3;&#x6811;Render Tree&#x3002;&#x672C;&#x8282;&#x6211;&#x4EEC;&#x5C06;&#x91CD;&#x70B9;&#x4ECB;&#x7ECD;&#x4E00;&#x4E0B;<code>RenderObject</code>&#x7684;&#x4F5C;&#x7528;&#x3002;</p>
<p><code>RenderObject</code>&#x5C31;&#x662F;&#x6E32;&#x67D3;&#x6811;&#x4E2D;&#x7684;&#x4E00;&#x4E2A;&#x5BF9;&#x8C61;&#xFF0C;&#x5B83;&#x62E5;&#x6709;&#x4E00;&#x4E2A;<code>parent</code>&#x548C;&#x4E00;&#x4E2A;<code>parentData</code> &#x63D2;&#x69FD;&#xFF08;slot&#xFF09;&#xFF0C;&#x6240;&#x8C13;&#x63D2;&#x69FD;&#xFF0C;&#x5C31;&#x662F;&#x6307;&#x9884;&#x7559;&#x7684;&#x4E00;&#x4E2A;&#x63A5;&#x53E3;&#x6216;&#x4F4D;&#x7F6E;&#xFF0C;&#x8FD9;&#x4E2A;&#x63A5;&#x53E3;&#x548C;&#x4F4D;&#x7F6E;&#x662F;&#x7531;&#x5176;&#x5B83;&#x5BF9;&#x8C61;&#x6765;&#x63A5;&#x5165;&#x6216;&#x5360;&#x636E;&#x7684;&#xFF0C;&#x8FD9;&#x4E2A;&#x63A5;&#x53E3;&#x6216;&#x4F4D;&#x7F6E;&#x5728;&#x8F6F;&#x4EF6;&#x4E2D;&#x901A;&#x5E38;&#x7528;&#x9884;&#x7559;&#x53D8;&#x91CF;&#x6765;&#x8868;&#x793A;&#xFF0C;&#x800C;<code>parentData</code>&#x6B63;&#x662F;&#x4E00;&#x4E2A;&#x9884;&#x7559;&#x53D8;&#x91CF;&#xFF0C;&#x5B83;&#x6B63;&#x662F;&#x7531;<code>parent</code> &#x6765;&#x8D4B;&#x503C;&#x7684;&#xFF0C;<code>parent</code>&#x901A;&#x5E38;&#x4F1A;&#x901A;&#x8FC7;&#x5B50;<code>RenderObject</code>&#x7684;<code>parentData</code>&#x5B58;&#x50A8;&#x4E00;&#x4E9B;&#x548C;&#x5B50;&#x5143;&#x7D20;&#x76F8;&#x5173;&#x7684;&#x6570;&#x636E;&#xFF0C;&#x5982;&#x5728;Stack&#x5E03;&#x5C40;&#x4E2D;&#xFF0C;<code>RenderStack</code>&#x5C31;&#x4F1A;&#x5C06;&#x5B50;&#x5143;&#x7D20;&#x7684;&#x504F;&#x79FB;&#x6570;&#x636E;&#x5B58;&#x50A8;&#x5728;&#x5B50;&#x5143;&#x7D20;&#x7684;<code>parentData</code>&#x4E2D;&#xFF08;&#x5177;&#x4F53;&#x53EF;&#x4EE5;&#x67E5;&#x770B;<code>Positioned</code>&#x5B9E;&#x73B0;&#xFF09;&#x3002;</p>
<p><code>RenderObject</code>&#x7C7B;&#x672C;&#x8EAB;&#x5B9E;&#x73B0;&#x4E86;&#x4E00;&#x5957;&#x57FA;&#x7840;&#x7684;layout&#x548C;&#x7ED8;&#x5236;&#x534F;&#x8BAE;&#xFF0C;&#x4F46;&#x662F;&#x5E76;&#x6CA1;&#x6709;&#x5B9A;&#x4E49;&#x5B50;&#x8282;&#x70B9;&#x6A21;&#x578B;&#xFF08;&#x5982;&#x4E00;&#x4E2A;&#x8282;&#x70B9;&#x53EF;&#x4EE5;&#x6709;&#x51E0;&#x4E2A;&#x5B50;&#x8282;&#x70B9;&#xFF0C;&#x6CA1;&#x6709;&#x5B50;&#x8282;&#x70B9;&#xFF1F;&#x4E00;&#x4E2A;&#xFF1F;&#x4E24;&#x4E2A;&#xFF1F;&#x6216;&#x8005;&#x66F4;&#x591A;&#xFF1F;&#xFF09;&#x3002; &#x5B83;&#x4E5F;&#x6CA1;&#x6709;&#x5B9A;&#x4E49;&#x5750;&#x6807;&#x7CFB;&#x7EDF;&#xFF08;&#x5982;&#x5B50;&#x8282;&#x70B9;&#x5B9A;&#x4F4D;&#x662F;&#x5728;&#x7B1B;&#x5361;&#x5C14;&#x5750;&#x6807;&#x4E2D;&#x8FD8;&#x662F;&#x6781;&#x5750;&#x6807;&#xFF1F;&#xFF09;&#x548C;&#x5177;&#x4F53;&#x7684;&#x5E03;&#x5C40;&#x534F;&#x8BAE;&#xFF08;&#x662F;&#x901A;&#x8FC7;&#x5BBD;&#x9AD8;&#x8FD8;&#x662F;&#x901A;&#x8FC7;constraint&#x548C;size?&#xFF0C;&#x6216;&#x8005;&#x662F;&#x5426;&#x7531;&#x7236;&#x8282;&#x70B9;&#x5728;&#x5B50;&#x8282;&#x70B9;&#x5E03;&#x5C40;&#x4E4B;&#x524D;&#x6216;&#x4E4B;&#x540E;&#x8BBE;&#x7F6E;&#x5B50;&#x8282;&#x70B9;&#x7684;&#x5927;&#x5C0F;&#x548C;&#x4F4D;&#x7F6E;&#x7B49;&#xFF09;&#x3002;&#x4E3A;&#x6B64;&#xFF0C;Flutter&#x63D0;&#x4F9B;&#x4E86;&#x4E00;&#x4E2A;<code>RenderBox</code>&#x7C7B;&#xFF0C;&#x5B83;&#x7EE7;&#x627F;&#x81EA;<code>`RenderObject</code>&#xFF0C;&#x5E03;&#x5C40;&#x5750;&#x6807;&#x7CFB;&#x7EDF;&#x91C7;&#x7528;&#x7B1B;&#x5361;&#x5C14;&#x5750;&#x6807;&#x7CFB;&#xFF0C;&#x8FD9;&#x548C;Android&#x548C;iOS&#x539F;&#x751F;&#x5750;&#x6807;&#x7CFB;&#x662F;&#x4E00;&#x81F4;&#x7684;&#xFF0C;&#x90FD;&#x662F;&#x5C4F;&#x5E55;&#x7684;top&#x3001;left&#x662F;&#x539F;&#x70B9;&#xFF0C;&#x7136;&#x540E;&#x5206;&#x5BBD;&#x9AD8;&#x4E24;&#x4E2A;&#x8F74;&#xFF0C;&#x5927;&#x591A;&#x6570;&#x60C5;&#x51B5;&#x4E0B;&#xFF0C;&#x6211;&#x4EEC;&#x76F4;&#x63A5;&#x4F7F;&#x7528;<code>RenderBox</code>&#x5C31;&#x53EF;&#x4EE5;&#x4E86;&#xFF0C;&#x9664;&#x975E;&#x9047;&#x5230;&#x8981;&#x81EA;&#x5B9A;&#x4E49;&#x5E03;&#x5C40;&#x6A21;&#x578B;&#x6216;&#x5750;&#x6807;&#x7CFB;&#x7EDF;&#x7684;&#x60C5;&#x51B5;&#xFF0C;&#x4E0B;&#x9762;&#x6211;&#x4EEC;&#x91CD;&#x70B9;&#x4ECB;&#x7ECD;&#x4E00;&#x4E0B;<code>RenderBox</code>&#x3002;</p>
<h2 id="1431-&#x5E03;&#x5C40;&#x8FC7;&#x7A0B;">14.3.1 &#x5E03;&#x5C40;&#x8FC7;&#x7A0B;</h2>
<h3 id="constraints">Constraints</h3>
<p>&#x5728;<code>RenderBox</code> &#x4E2D;&#xFF0C;&#x6709;&#x4E2A;<code>size</code>&#x5C5E;&#x6027;&#x7528;&#x6765;&#x4FDD;&#x5B58;&#x63A7;&#x4EF6;&#x7684;&#x5BBD;&#x548C;&#x9AD8;&#x3002;<code>RenderBox</code>&#x7684;layout&#x662F;&#x901A;&#x8FC7;&#x5728;&#x7EC4;&#x4EF6;&#x6811;&#x4E2D;&#x4ECE;&#x4E0A;&#x5F80;&#x4E0B;&#x4F20;&#x9012;<code>BoxConstraints</code>&#x5BF9;&#x8C61;&#x7684;&#x5B9E;&#x73B0;&#x7684;&#x3002;<code>BoxConstraints</code>&#x5BF9;&#x8C61;&#x53EF;&#x4EE5;&#x9650;&#x5236;&#x5B50;&#x8282;&#x70B9;&#x7684;&#x6700;&#x5927;&#x548C;&#x6700;&#x5C0F;&#x5BBD;&#x9AD8;&#xFF0C;&#x5B50;&#x8282;&#x70B9;&#x5FC5;&#x987B;&#x9075;&#x5B88;&#x7236;&#x8282;&#x70B9;&#x7ED9;&#x5B9A;&#x7684;&#x9650;&#x5236;&#x6761;&#x4EF6;&#x3002;</p>
<p>&#x5728;&#x5E03;&#x5C40;&#x9636;&#x6BB5;&#xFF0C;&#x7236;&#x8282;&#x70B9;&#x4F1A;&#x8C03;&#x7528;&#x5B50;&#x8282;&#x70B9;&#x7684;<code>layout()</code>&#x65B9;&#x6CD5;&#xFF0C;&#x4E0B;&#x9762;&#x6211;&#x4EEC;&#x770B;&#x770B;<code>RenderObject</code>&#x4E2D;<code>layout()</code>&#x65B9;&#x6CD5;&#x7684;&#x5927;&#x81F4;&#x5B9E;&#x73B0;&#xFF08;&#x5220;&#x6389;&#x4E86;&#x4E00;&#x4E9B;&#x65E0;&#x5173;&#x4EE3;&#x7801;&#x548C;&#x5F02;&#x5E38;&#x6355;&#x83B7;&#xFF09;:</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">void</span> <span class="token function">layout</span><span class="token punctuation">(</span>Constraints constraints<span class="token punctuation">,</span> <span class="token punctuation">{</span> bool parentUsesSize <span class="token operator">=</span> <span class="token boolean">false</span> <span class="token punctuation">}</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
   <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
   RenderObject relayoutBoundary<span class="token punctuation">;</span> 
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>parentUsesSize <span class="token operator">||</span> sizedByParent <span class="token operator">||</span> constraints<span class="token punctuation">.</span>isTight 
        <span class="token operator">||</span> parent <span class="token operator">is!</span> RenderObject<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      relayoutBoundary <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
      <span class="token keyword">final</span> RenderObject parent <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>parent<span class="token punctuation">;</span>
      relayoutBoundary <span class="token operator">=</span> parent<span class="token punctuation">.</span>_relayoutBoundary<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>sizedByParent<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">performResize</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token function">performLayout</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x53EF;&#x4EE5;&#x770B;&#x5230;<code>layout</code>&#x65B9;&#x6CD5;&#x9700;&#x8981;&#x4F20;&#x5165;&#x4E24;&#x4E2A;&#x53C2;&#x6570;&#xFF0C;&#x7B2C;&#x4E00;&#x4E2A;&#x4E3A;<code>constraints</code>&#xFF0C;&#x5373; &#x7236;&#x8282;&#x70B9;&#x5BF9;&#x5B50;&#x8282;&#x70B9;&#x5927;&#x5C0F;&#x7684;&#x9650;&#x5236;&#xFF0C;&#x8BE5;&#x503C;&#x6839;&#x636E;&#x7236;&#x8282;&#x70B9;&#x7684;&#x5E03;&#x5C40;&#x903B;&#x8F91;&#x786E;&#x5B9A;&#x3002;&#x53E6;&#x5916;&#x4E00;&#x4E2A;&#x53C2;&#x6570;&#x662F; <code>parentUsesSize</code>&#xFF0C;&#x8BE5;&#x503C;&#x7528;&#x4E8E;&#x786E;&#x5B9A; <code>relayoutBoundary</code>&#xFF0C;&#x8BE5;&#x53C2;&#x6570;&#x8868;&#x793A;&#x5B50;&#x8282;&#x70B9;&#x5E03;&#x5C40;&#x53D8;&#x5316;&#x662F;&#x5426;&#x5F71;&#x54CD;&#x7236;&#x8282;&#x70B9;&#xFF0C;&#x5982;&#x679C;&#x4E3A;<code>true</code>&#xFF0C;&#x5F53;&#x5B50;&#x8282;&#x70B9;&#x5E03;&#x5C40;&#x53D1;&#x751F;&#x53D8;&#x5316;&#x65F6;&#x7236;&#x8282;&#x70B9;&#x90FD;&#x4F1A;&#x6807;&#x8BB0;&#x4E3A;&#x9700;&#x8981;&#x91CD;&#x65B0;&#x5E03;&#x5C40;&#xFF0C;&#x5982;&#x679C;&#x4E3A;<code>false</code>&#xFF0C;&#x5219;&#x5B50;&#x8282;&#x70B9;&#x5E03;&#x5C40;&#x53D1;&#x751F;&#x53D8;&#x5316;&#x540E;&#x4E0D;&#x4F1A;&#x5F71;&#x54CD;&#x7236;&#x8282;&#x70B9;&#x3002;</p>
<h4 id="relayoutboundary">relayoutBoundary</h4>
<p>&#x4E0A;&#x9762;<code>layout()</code>&#x6E90;&#x7801;&#x4E2D;&#x5B9A;&#x4E49;&#x4E86;&#x4E00;&#x4E2A;<code>relayoutBoundary</code>&#x53D8;&#x91CF;&#xFF0C;&#x4EC0;&#x4E48;&#x662F; <code>relayoutBoundary</code>&#xFF1F;&#x5728;&#x524D;&#x9762;&#x4ECB;&#x7ECD;<code>Element</code>&#x65F6;&#xFF0C;&#x6211;&#x4EEC;&#x8BB2;&#x8FC7;&#x5F53;&#x4E00;&#x4E2A;<code>Element</code>&#x6807;&#x8BB0;&#x4E3A; dirty &#x65F6;&#x4FBF;&#x4F1A;&#x91CD;&#x65B0;build&#xFF0C;&#x8FD9;&#x65F6;<code>RenderObject</code>&#x4FBF;&#x4F1A;&#x91CD;&#x65B0;&#x5E03;&#x5C40;&#xFF0C;&#x6211;&#x4EEC;&#x662F;&#x901A;&#x8FC7;&#x8C03;&#x7528; <code>markNeedsBuild()</code> &#x6765;&#x6807;&#x8BB0;<code>Element</code>&#x4E3A;dirty&#x7684;&#x3002;&#x5728;<code>RenderObject</code>&#x4E2D;&#x6709;&#x4E00;&#x4E2A;&#x7C7B;&#x4F3C;&#x7684;<code>markNeedsLayout()</code>&#x65B9;&#x6CD5;&#xFF0C;&#x5B83;&#x4F1A;&#x5C06;<code>RenderObject</code>&#x7684;&#x5E03;&#x5C40;&#x72B6;&#x6001;&#x6807;&#x8BB0;&#x4E3A; dirty&#xFF0C;&#x8FD9;&#x6837;&#x5728;&#x4E0B;&#x4E00;&#x4E2A;frame&#x4E2D;&#x4FBF;&#x4F1A;&#x91CD;&#x65B0;layout&#xFF0C;&#x6211;&#x4EEC;&#x770B;&#x770B;<code>RenderObject</code>&#x7684;<code>markNeedsLayout()</code>&#x7684;&#x90E8;&#x5206;&#x6E90;&#x7801;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">void</span> <span class="token function">markNeedsLayout</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
  <span class="token keyword">assert</span><span class="token punctuation">(</span>_relayoutBoundary <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>_relayoutBoundary <span class="token operator">!=</span> <span class="token keyword">this</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token function">markParentNeedsLayout</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    _needsLayout <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>owner <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
      owner<span class="token punctuation">.</span>_nodesNeedingLayout<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      owner<span class="token punctuation">.</span><span class="token function">requestVisualUpdate</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x4EE3;&#x7801;&#x5927;&#x81F4;&#x903B;&#x8F91;&#x662F;&#x5148;&#x5224;&#x65AD;&#x81EA;&#x8EAB;&#x662F;&#x4E0D;&#x662F;<code>relayoutBoundary</code>&#xFF0C;&#x5982;&#x679C;&#x4E0D;&#x662F;&#x5C31;&#x7EE7;&#x7EED;&#x5411;parent &#x67E5;&#x627E;&#xFF0C;&#x4E00;&#x76F4;&#x5411;&#x4E0A;&#x67E5;&#x627E;&#x5230;&#x662F; <code>relayoutBoundary</code> &#x7684; <code>RenderObject</code>&#x4E3A;&#x6B62;&#xFF0C;&#x7136;&#x540E;&#x518D;&#x5C06;&#x5176;&#x6807;&#x8BB0;&#x4E3A; dirty &#x7684;&#x3002;&#x8FD9;&#x6837;&#x6765;&#x770B;&#x5B83;&#x7684;&#x4F5C;&#x7528;&#x5C31;&#x6BD4;&#x8F83;&#x660E;&#x663E;&#x4E86;&#xFF0C;&#x610F;&#x601D;&#x5C31;&#x662F;&#x5F53;&#x4E00;&#x4E2A;&#x63A7;&#x4EF6;&#x7684;&#x5927;&#x5C0F;&#x88AB;&#x6539;&#x53D8;&#x65F6;&#x53EF;&#x80FD;&#x4F1A;&#x5F71;&#x54CD;&#x5230;&#x5B83;&#x7684; parent&#xFF0C;&#x56E0;&#x6B64; parent &#x4E5F;&#x9700;&#x8981;&#x88AB;&#x91CD;&#x65B0;&#x5E03;&#x5C40;&#xFF0C;&#x90A3;&#x4E48;&#x5230;&#x4EC0;&#x4E48;&#x65F6;&#x5019;&#x662F;&#x4E2A;&#x5934;&#x5462;&#xFF1F;&#x7B54;&#x6848;&#x5C31;&#x662F; <code>relayoutBoundary</code>&#xFF0C;&#x5982;&#x679C;&#x4E00;&#x4E2A; <code>RenderObject</code> &#x662F; <code>relayoutBoundary</code>&#xFF0C;&#x5C31;&#x8868;&#x793A;&#x5B83;&#x7684;&#x5927;&#x5C0F;&#x53D8;&#x5316;&#x4E0D;&#x4F1A;&#x518D;&#x5F71;&#x54CD;&#x5230; parent &#x7684;&#x5927;&#x5C0F;&#x4E86;&#xFF0C;&#x4E8E;&#x662F; parent &#x4E5F;&#x5C31;&#x4E0D;&#x7528;&#x91CD;&#x65B0;&#x5E03;&#x5C40;&#x4E86;&#x3002;</p>
<h4 id="performresize-&#x548C;-performlayout">performResize &#x548C; performLayout</h4>
<p><code>RenderBox</code>&#x5B9E;&#x9645;&#x7684;&#x6D4B;&#x91CF;&#x548C;&#x5E03;&#x5C40;&#x903B;&#x8F91;&#x662F;&#x5728;<code>performResize()</code> &#x548C; <code>performLayout()</code>&#x4E24;&#x4E2A;&#x65B9;&#x6CD5;&#x4E2D;&#xFF0C;RenderBox&#x5B50;&#x7C7B;&#x9700;&#x8981;&#x5B9E;&#x73B0;&#x8FD9;&#x4E24;&#x4E2A;&#x65B9;&#x6CD5;&#x6765;&#x5B9A;&#x5236;&#x81EA;&#x8EAB;&#x7684;&#x5E03;&#x5C40;&#x903B;&#x8F91;&#x3002;&#x6839;&#x636E;<code>layout()</code> &#x6E90;&#x7801;&#x53EF;&#x4EE5;&#x770B;&#x51FA;&#x53EA;&#x6709; <code>sizedByParent</code> &#x4E3A; <code>true</code> &#x65F6;&#xFF0C;<code>performResize()</code> &#x624D;&#x4F1A;&#x88AB;&#x8C03;&#x7528;&#xFF0C;&#x800C; <code>performLayout()</code> &#x662F;&#x6BCF;&#x6B21;&#x5E03;&#x5C40;&#x90FD;&#x4F1A;&#x88AB;&#x8C03;&#x7528;&#x7684;&#x3002;<code>sizedByParent</code> &#x610F;&#x4E3A;&#x8BE5;&#x8282;&#x70B9;&#x7684;&#x5927;&#x5C0F;&#x662F;&#x5426;&#x4EC5;&#x901A;&#x8FC7; parent &#x4F20;&#x7ED9;&#x5B83;&#x7684; constraints &#x5C31;&#x53EF;&#x4EE5;&#x786E;&#x5B9A;&#x4E86;&#xFF0C;&#x5373;&#x8BE5;&#x8282;&#x70B9;&#x7684;&#x5927;&#x5C0F;&#x4E0E;&#x5B83;&#x81EA;&#x8EAB;&#x7684;&#x5C5E;&#x6027;&#x548C;&#x5176;&#x5B50;&#x8282;&#x70B9;&#x65E0;&#x5173;&#xFF0C;&#x6BD4;&#x5982;&#x5982;&#x679C;&#x4E00;&#x4E2A;&#x63A7;&#x4EF6;&#x6C38;&#x8FDC;&#x5145;&#x6EE1; parent &#x7684;&#x5927;&#x5C0F;&#xFF0C;&#x90A3;&#x4E48; <code>sizedByParent</code>&#x5C31;&#x5E94;&#x8BE5;&#x8FD4;&#x56DE;<code>true</code>&#xFF0C;&#x6B64;&#x65F6;&#x5176;&#x5927;&#x5C0F;&#x5728; <code>performResize()</code> &#x4E2D;&#x5C31;&#x786E;&#x5B9A;&#x4E86;&#xFF0C;&#x5728;&#x540E;&#x9762;&#x7684; <code>performLayout()</code> &#x65B9;&#x6CD5;&#x4E2D;&#x5C06;&#x4E0D;&#x4F1A;&#x518D;&#x88AB;&#x4FEE;&#x6539;&#x4E86;&#xFF0C;&#x8FD9;&#x79CD;&#x60C5;&#x51B5;&#x4E0B; <code>performLayout()</code> &#x53EA;&#x8D1F;&#x8D23;&#x5E03;&#x5C40;&#x5B50;&#x8282;&#x70B9;&#x3002;</p>
<p>&#x5728; <code>performLayout()</code> &#x65B9;&#x6CD5;&#x4E2D;&#x9664;&#x4E86;&#x5B8C;&#x6210;&#x81EA;&#x8EAB;&#x5E03;&#x5C40;&#xFF0C;&#x4E5F;&#x5FC5;&#x987B;&#x5B8C;&#x6210;&#x5B50;&#x8282;&#x70B9;&#x7684;&#x5E03;&#x5C40;&#xFF0C;&#x8FD9;&#x662F;&#x56E0;&#x4E3A;&#x53EA;&#x6709;&#x7236;&#x5B50;&#x8282;&#x70B9;&#x5168;&#x90E8;&#x5B8C;&#x6210;&#x540E;&#x5E03;&#x5C40;&#x6D41;&#x7A0B;&#x624D;&#x7B97;&#x771F;&#x6B63;&#x5B8C;&#x6210;&#x3002;&#x6240;&#x4EE5;&#x6700;&#x7EC8;&#x7684;&#x8C03;&#x7528;&#x6808;&#x5C06;&#x4F1A;&#x53D8;&#x6210;&#xFF1A;<em>layout() &gt; performResize()/performLayout() &gt; child.layout() &gt; ...</em>  &#xFF0C;&#x5982;&#x6B64;&#x9012;&#x5F52;&#x5B8C;&#x6210;&#x6574;&#x4E2A;UI&#x7684;&#x5E03;&#x5C40;&#x3002;</p>
<p><code>RenderBox</code>&#x5B50;&#x7C7B;&#x8981;&#x5B9A;&#x5236;&#x5E03;&#x5C40;&#x7B97;&#x6CD5;&#x4E0D;&#x5E94;&#x8BE5;&#x91CD;&#x5199;<code>layout()</code>&#x65B9;&#x6CD5;&#xFF0C;&#x56E0;&#x4E3A;&#x5BF9;&#x4E8E;&#x4EFB;&#x4F55;RenderBox&#x7684;&#x5B50;&#x7C7B;&#x6765;&#x8BF4;&#xFF0C;&#x5B83;&#x7684;layout&#x6D41;&#x7A0B;&#x57FA;&#x672C;&#x662F;&#x76F8;&#x540C;&#x7684;&#xFF0C;&#x4E0D;&#x540C;&#x4E4B;&#x5904;&#x53EA;&#x5728;&#x5177;&#x4F53;&#x7684;&#x5E03;&#x5C40;&#x7B97;&#x6CD5;&#xFF0C;&#x800C;&#x5177;&#x4F53;&#x7684;&#x5E03;&#x5C40;&#x7B97;&#x6CD5;&#x5B50;&#x7C7B;&#x5E94;&#x8BE5;&#x901A;&#x8FC7;&#x91CD;&#x5199;<code>performResize()</code> &#x548C; <code>performLayout()</code>&#x4E24;&#x4E2A;&#x65B9;&#x6CD5;&#x6765;&#x5B9E;&#x73B0;&#xFF0C;&#x4ED6;&#x4EEC;&#x4F1A;&#x5728;<code>layout()</code>&#x4E2D;&#x88AB;&#x8C03;&#x7528;&#x3002;</p>
<h4 id="parentdata">ParentData</h4>
<p>&#x5F53;layout&#x7ED3;&#x675F;&#x540E;&#xFF0C;&#x6BCF;&#x4E2A;&#x8282;&#x70B9;&#x7684;&#x4F4D;&#x7F6E;&#xFF08;&#x76F8;&#x5BF9;&#x4E8E;&#x7236;&#x8282;&#x70B9;&#x7684;&#x504F;&#x79FB;&#xFF09;&#x5C31;&#x5DF2;&#x7ECF;&#x786E;&#x5B9A;&#x4E86;&#xFF0C;<code>RenderObject</code>&#x5C31;&#x53EF;&#x4EE5;&#x6839;&#x636E;&#x4F4D;&#x7F6E;&#x4FE1;&#x606F;&#x6765;&#x8FDB;&#x884C;&#x6700;&#x7EC8;&#x7684;&#x7ED8;&#x5236;&#x3002;&#x4F46;&#x662F;&#x5728;layout&#x8FC7;&#x7A0B;&#x4E2D;&#xFF0C;&#x8282;&#x70B9;&#x7684;&#x4F4D;&#x7F6E;&#x4FE1;&#x606F;&#x600E;&#x4E48;&#x4FDD;&#x5B58;&#xFF1F;&#x5BF9;&#x4E8E;&#x5927;&#x591A;&#x6570;<code>RenderBox</code>&#x5B50;&#x7C7B;&#x6765;&#x8BF4;&#x5982;&#x679C;&#x5B50;&#x7C7B;&#x53EA;&#x6709;&#x4E00;&#x4E2A;&#x5B50;&#x8282;&#x70B9;&#xFF0C;&#x90A3;&#x4E48;&#x5B50;&#x8282;&#x70B9;&#x504F;&#x79FB;&#x4E00;&#x822C;&#x90FD;&#x662F;<code>Offset.zero</code> &#xFF0C;&#x5982;&#x679C;&#x6709;&#x591A;&#x4E2A;&#x5B50;&#x8282;&#x70B9;&#xFF0C;&#x5219;&#x6BCF;&#x4E2A;&#x5B50;&#x8282;&#x70B9;&#x7684;&#x504F;&#x79FB;&#x5C31;&#x53EF;&#x80FD;&#x4E0D;&#x540C;&#x3002;&#x800C;&#x5B50;&#x8282;&#x70B9;&#x5728;&#x7236;&#x8282;&#x70B9;&#x7684;&#x504F;&#x79FB;&#x6570;&#x636E;&#x6B63;&#x662F;&#x901A;&#x8FC7;<code>RenderObject</code>&#x7684;<code>parentData</code>&#x5C5E;&#x6027;&#x6765;&#x4FDD;&#x5B58;&#x7684;&#x3002;&#x5728;<code>RenderBox</code>&#x4E2D;&#xFF0C;&#x5176;<code>parentData</code>&#x5C5E;&#x6027;&#x9ED8;&#x8BA4;&#x662F;&#x4E00;&#x4E2A;<code>BoxParentData</code>&#x5BF9;&#x8C61;&#xFF0C;&#x8BE5;&#x5C5E;&#x6027;&#x53EA;&#x80FD;&#x901A;&#x8FC7;&#x7236;&#x8282;&#x70B9;&#x7684;<code>setupParentData()</code>&#x65B9;&#x6CD5;&#x6765;&#x8BBE;&#x7F6E;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">abstract</span> <span class="token keyword">class</span> <span class="token class-name">RenderBox</span> <span class="token keyword">extends</span> <span class="token class-name">RenderObject</span> <span class="token punctuation">{</span>
  <span class="token metadata symbol">@override</span>
  <span class="token keyword">void</span> <span class="token function">setupParentData</span><span class="token punctuation">(</span>covariant RenderObject child<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>child<span class="token punctuation">.</span>parentData <span class="token operator">is!</span> BoxParentData<span class="token punctuation">)</span>
      child<span class="token punctuation">.</span>parentData <span class="token operator">=</span> <span class="token function">BoxParentData</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span>
</code></pre>
<p><code>BoxParentData</code>&#x5B9A;&#x4E49;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token comment">/// Parentdata &#x4F1A;&#x88AB;RenderBox&#x548C;&#x5B83;&#x7684;&#x5B50;&#x7C7B;&#x4F7F;&#x7528;.</span>
<span class="token keyword">class</span> <span class="token class-name">BoxParentData</span> <span class="token keyword">extends</span> <span class="token class-name">ParentData</span> <span class="token punctuation">{</span>
  <span class="token comment">/// offset&#x8868;&#x793A;&#x5728;&#x5B50;&#x8282;&#x70B9;&#x5728;&#x7236;&#x8282;&#x70B9;&#x5750;&#x6807;&#x7CFB;&#x4E2D;&#x7684;&#x7ED8;&#x5236;&#x504F;&#x79FB;  </span>
  Offset offset <span class="token operator">=</span> Offset<span class="token punctuation">.</span>zero<span class="token punctuation">;</span>

  <span class="token metadata symbol">@override</span>
  String <span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token string">&apos;offset=$offset&apos;</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<blockquote>
<p>&#x4E00;&#x5B9A;&#x8981;&#x6CE8;&#x610F;&#xFF0C;<code>RenderObject</code>&#x7684;<code>parentData</code> &#x53EA;&#x80FD;&#x901A;&#x8FC7;&#x7236;&#x5143;&#x7D20;&#x8BBE;&#x7F6E;.</p>
</blockquote>
<p>&#x5F53;&#x7136;&#xFF0C;<code>ParentData</code>&#x5E76;&#x4E0D;&#x4EC5;&#x4EC5;&#x53EF;&#x4EE5;&#x7528;&#x6765;&#x5B58;&#x50A8;&#x504F;&#x79FB;&#x4FE1;&#x606F;&#xFF0C;&#x901A;&#x5E38;&#x6240;&#x6709;&#x548C;&#x5B50;&#x8282;&#x70B9;&#x7279;&#x5B9A;&#x7684;&#x6570;&#x636E;&#x90FD;&#x53EF;&#x4EE5;&#x5B58;&#x50A8;&#x5230;&#x5B50;&#x8282;&#x70B9;&#x7684;<code>ParentData</code>&#x4E2D;&#xFF0C;&#x5982;<code>ContainerBox</code>&#x7684;<code>ParentData</code>&#x5C31;&#x4FDD;&#x5B58;&#x4E86;&#x6307;&#x5411;&#x5144;&#x5F1F;&#x8282;&#x70B9;&#x7684;<code>previousSibling</code>&#x548C;<code>nextSibling</code>&#xFF0C;<code>Element.visitChildren()</code>&#x65B9;&#x6CD5;&#x4E5F;&#x6B63;&#x662F;&#x901A;&#x8FC7;&#x5B83;&#x4EEC;&#x6765;&#x5B9E;&#x73B0;&#x5BF9;&#x5B50;&#x8282;&#x70B9;&#x7684;&#x904D;&#x5386;&#x3002;&#x518D;&#x6BD4;&#x5982;<code>KeepAlive</code> &#x7EC4;&#x4EF6;&#xFF0C;&#x5B83;&#x4F7F;&#x7528;<code>KeepAliveParentDataMixin</code>&#xFF08;&#x7EE7;&#x627F;&#x81EA;<code>ParentData</code>&#xFF09; &#x6765;&#x4FDD;&#x5B58;&#x5B50;&#x8282;&#x7684;<code>keepAlive</code>&#x72B6;&#x6001;&#x3002;</p>
<h2 id="1432-&#x7ED8;&#x5236;&#x8FC7;&#x7A0B;">14.3.2 &#x7ED8;&#x5236;&#x8FC7;&#x7A0B;</h2>
<p><code>RenderObject</code>&#x53EF;&#x4EE5;&#x901A;&#x8FC7;<code>paint()</code>&#x65B9;&#x6CD5;&#x6765;&#x5B8C;&#x6210;&#x5177;&#x4F53;&#x7ED8;&#x5236;&#x903B;&#x8F91;&#xFF0C;&#x6D41;&#x7A0B;&#x548C;&#x5E03;&#x5C40;&#x6D41;&#x7A0B;&#x76F8;&#x4F3C;&#xFF0C;&#x5B50;&#x7C7B;&#x53EF;&#x4EE5;&#x5B9E;&#x73B0;<code>paint()</code>&#x65B9;&#x6CD5;&#x6765;&#x5B8C;&#x6210;&#x81EA;&#x8EAB;&#x7684;&#x7ED8;&#x5236;&#x903B;&#x8F91;&#xFF0C;<code>paint()</code>&#x7B7E;&#x540D;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">void</span> <span class="token function">paint</span><span class="token punctuation">(</span>PaintingContext context<span class="token punctuation">,</span> Offset offset<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token punctuation">}</span>
</code></pre>
<p>&#x901A;&#x8FC7;<code>context.canvas</code>&#x53EF;&#x4EE5;&#x53D6;&#x5230;<code>Canvas</code>&#x5BF9;&#x8C61;&#xFF0C;&#x63A5;&#x4E0B;&#x6765;&#x5C31;&#x53EF;&#x4EE5;&#x8C03;&#x7528;<code>Canvas</code> API&#x6765;&#x5B9E;&#x73B0;&#x5177;&#x4F53;&#x7684;&#x7ED8;&#x5236;&#x903B;&#x8F91;&#x3002;</p>
<p>&#x5982;&#x679C;&#x8282;&#x70B9;&#x6709;&#x5B50;&#x8282;&#x70B9;&#xFF0C;&#x5B83;&#x9664;&#x4E86;&#x5B8C;&#x6210;&#x81EA;&#x8EAB;&#x7ED8;&#x5236;&#x903B;&#x8F91;&#x4E4B;&#x5916;&#xFF0C;&#x8FD8;&#x8981;&#x8C03;&#x7528;&#x5B50;&#x8282;&#x70B9;&#x7684;&#x7ED8;&#x5236;&#x65B9;&#x6CD5;&#x3002;&#x6211;&#x4EEC;&#x4EE5;<code>RenderFlex</code>&#x5BF9;&#x8C61;&#x4E3A;&#x4F8B;&#x8BF4;&#x660E;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token metadata symbol">@override</span>
<span class="token keyword">void</span> <span class="token function">paint</span><span class="token punctuation">(</span>PaintingContext context<span class="token punctuation">,</span> Offset offset<span class="token punctuation">)</span> <span class="token punctuation">{</span>

  <span class="token comment">// &#x5982;&#x679C;&#x5B50;&#x5143;&#x7D20;&#x672A;&#x8D85;&#x51FA;&#x5F53;&#x524D;&#x8FB9;&#x754C;&#xFF0C;&#x5219;&#x7ED8;&#x5236;&#x5B50;&#x5143;&#x7D20;  </span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>_overflow <span class="token operator">&lt;=</span> <span class="token number">0.0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token function">defaultPaint</span><span class="token punctuation">(</span>context<span class="token punctuation">,</span> offset<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>

  <span class="token comment">// &#x5982;&#x679C;size&#x4E3A;&#x7A7A;&#xFF0C;&#x5219;&#x65E0;&#x9700;&#x7ED8;&#x5236;</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>size<span class="token punctuation">.</span>isEmpty<span class="token punctuation">)</span>
    <span class="token keyword">return</span><span class="token punctuation">;</span>

  <span class="token comment">// &#x526A;&#x88C1;&#x6389;&#x6EA2;&#x51FA;&#x8FB9;&#x754C;&#x7684;&#x90E8;&#x5206;</span>
  context<span class="token punctuation">.</span><span class="token function">pushClipRect</span><span class="token punctuation">(</span>needsCompositing<span class="token punctuation">,</span> offset<span class="token punctuation">,</span> Offset<span class="token punctuation">.</span>zero <span class="token operator">&amp;</span> size<span class="token punctuation">,</span> defaultPaint<span class="token punctuation">)</span><span class="token punctuation">;</span>

  <span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">final</span> String debugOverflowHints <span class="token operator">=</span> <span class="token string">&apos;...&apos;</span><span class="token punctuation">;</span> <span class="token comment">//&#x6EA2;&#x51FA;&#x63D0;&#x793A;&#x5185;&#x5BB9;&#xFF0C;&#x7701;&#x7565;</span>
    <span class="token comment">// &#x7ED8;&#x5236;&#x6EA2;&#x51FA;&#x90E8;&#x5206;&#x7684;&#x9519;&#x8BEF;&#x63D0;&#x793A;&#x6837;&#x5F0F;</span>
    Rect overflowChildRect<span class="token punctuation">;</span>
    <span class="token keyword">switch</span> <span class="token punctuation">(</span>_direction<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">case</span> Axis<span class="token punctuation">.</span>horizontal<span class="token punctuation">:</span>
        overflowChildRect <span class="token operator">=</span> Rect<span class="token punctuation">.</span><span class="token function">fromLTWH</span><span class="token punctuation">(</span><span class="token number">0.0</span><span class="token punctuation">,</span> <span class="token number">0.0</span><span class="token punctuation">,</span> size<span class="token punctuation">.</span>width <span class="token operator">+</span> _overflow<span class="token punctuation">,</span> <span class="token number">0.0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">break</span><span class="token punctuation">;</span>
      <span class="token keyword">case</span> Axis<span class="token punctuation">.</span>vertical<span class="token punctuation">:</span>
        overflowChildRect <span class="token operator">=</span> Rect<span class="token punctuation">.</span><span class="token function">fromLTWH</span><span class="token punctuation">(</span><span class="token number">0.0</span><span class="token punctuation">,</span> <span class="token number">0.0</span><span class="token punctuation">,</span> <span class="token number">0.0</span><span class="token punctuation">,</span> size<span class="token punctuation">.</span>height <span class="token operator">+</span> _overflow<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">break</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>  
    <span class="token function">paintOverflowIndicator</span><span class="token punctuation">(</span>context<span class="token punctuation">,</span> offset<span class="token punctuation">,</span> Offset<span class="token punctuation">.</span>zero <span class="token operator">&amp;</span> size<span class="token punctuation">,</span>
                           overflowChildRect<span class="token punctuation">,</span> overflowHints<span class="token punctuation">:</span> debugOverflowHints<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x4EE3;&#x7801;&#x5F88;&#x7B80;&#x5355;&#xFF0C;&#x9996;&#x5148;&#x5224;&#x65AD;&#x6709;&#x65E0;&#x6EA2;&#x51FA;&#xFF0C;&#x5982;&#x679C;&#x6CA1;&#x6709;&#x5219;&#x8C03;&#x7528;<code>defaultPaint(context, offset)</code>&#x6765;&#x5B8C;&#x6210;&#x7ED8;&#x5236;&#xFF0C;&#x8BE5;&#x65B9;&#x6CD5;&#x6E90;&#x7801;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">void</span> <span class="token function">defaultPaint</span><span class="token punctuation">(</span>PaintingContext context<span class="token punctuation">,</span> Offset offset<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  ChildType child <span class="token operator">=</span> firstChild<span class="token punctuation">;</span>
  <span class="token keyword">while</span> <span class="token punctuation">(</span>child <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">final</span> ParentDataType childParentData <span class="token operator">=</span> child<span class="token punctuation">.</span>parentData<span class="token punctuation">;</span>
    <span class="token comment">//&#x7ED8;&#x5236;&#x5B50;&#x8282;&#x70B9;&#xFF0C; </span>
    context<span class="token punctuation">.</span><span class="token function">paintChild</span><span class="token punctuation">(</span>child<span class="token punctuation">,</span> childParentData<span class="token punctuation">.</span>offset <span class="token operator">+</span> offset<span class="token punctuation">)</span><span class="token punctuation">;</span>
    child <span class="token operator">=</span> childParentData<span class="token punctuation">.</span>nextSibling<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x5F88;&#x660E;&#x663E;&#xFF0C;&#x7531;&#x4E8E;Flex&#x672C;&#x8EAB;&#x6CA1;&#x6709;&#x9700;&#x8981;&#x7ED8;&#x5236;&#x7684;&#x4E1C;&#x897F;&#xFF0C;&#x6240;&#x4EE5;&#x76F4;&#x63A5;&#x904D;&#x5386;&#x5176;&#x5B50;&#x8282;&#x70B9;&#xFF0C;&#x7136;&#x540E;&#x8C03;&#x7528;<code>paintChild()</code>&#x6765;&#x7ED8;&#x5236;&#x5B50;&#x8282;&#x70B9;&#xFF0C;&#x540C;&#x65F6;&#x5C06;&#x5B50;&#x8282;&#x70B9;<code>ParentData</code>&#x4E2D;&#x5728;layout&#x9636;&#x6BB5;&#x4FDD;&#x5B58;&#x7684;offset&#x52A0;&#x4E0A;&#x81EA;&#x8EAB;&#x504F;&#x79FB;&#x4F5C;&#x4E3A;&#x7B2C;&#x4E8C;&#x4E2A;&#x53C2;&#x6570;&#x4F20;&#x9012;&#x7ED9;<code>paintChild()</code>&#x3002;&#x800C;&#x5982;&#x679C;&#x5B50;&#x8282;&#x70B9;&#x8FD8;&#x6709;&#x5B50;&#x8282;&#x70B9;&#x65F6;&#xFF0C;<code>paintChild()</code>&#x65B9;&#x6CD5;&#x8FD8;&#x4F1A;&#x8C03;&#x7528;&#x5B50;&#x8282;&#x70B9;&#x7684;<code>paint()</code>&#x65B9;&#x6CD5;&#xFF0C;&#x5982;&#x6B64;&#x9012;&#x5F52;&#x5B8C;&#x6210;&#x6574;&#x4E2A;&#x8282;&#x70B9;&#x6811;&#x7684;&#x7ED8;&#x5236;&#xFF0C;&#x6700;&#x7EC8;&#x8C03;&#x7528;&#x6808;&#x4E3A;&#xFF1A; <em>paint() &gt; paintChild() &gt; paint() ...</em> &#x3002;</p>
<p>&#x5F53;&#x9700;&#x8981;&#x7ED8;&#x5236;&#x7684;&#x5185;&#x5BB9;&#x5927;&#x5C0F;&#x6EA2;&#x51FA;&#x5F53;&#x524D;&#x7A7A;&#x95F4;&#x65F6;&#xFF0C;&#x5C06;&#x4F1A;&#x6267;&#x884C;<code>paintOverflowIndicator()</code> &#x6765;&#x7ED8;&#x5236;&#x6EA2;&#x51FA;&#x90E8;&#x5206;&#x63D0;&#x793A;&#xFF0C;&#x8FD9;&#x4E2A;&#x5C31;&#x662F;&#x6211;&#x4EEC;&#x7ECF;&#x5E38;&#x770B;&#x5230;&#x7684;&#x6EA2;&#x51FA;&#x63D0;&#x793A;&#xFF0C;&#x5982;&#x56FE;14-3&#x6240;&#x793A;&#xFF1A;</p>
<p><img src="https://pcdn.flutterchina.club/imgs/14-3.png" alt="overflow"></p>
<h3 id="repaintboundary">RepaintBoundary</h3>
<p>&#x6211;&#x4EEC;&#x5DF2;&#x7ECF;&#x5728;<code>CustomPaint</code>&#x4E00;&#x8282;&#x4E2D;&#x4ECB;&#x7ECD;&#x8FC7;<code>RepaintBoundary</code>&#xFF0C;&#x73B0;&#x5728;&#x6211;&#x4EEC;&#x6DF1;&#x5165;&#x7684;&#x4E86;&#x89E3;&#x4E00;&#x4E9B;&#x3002;&#x4E0E; <code>RelayoutBoundary</code> &#x76F8;&#x4F3C;&#xFF0C;<code>RepaintBoundary</code>&#x662F;&#x7528;&#x4E8E;&#x5728;&#x786E;&#x5B9A;&#x91CD;&#x7ED8;&#x8FB9;&#x754C;&#x7684;&#xFF0C;&#x4E0E;<code>RelayoutBoundary</code>&#x4E0D;&#x540C;&#x7684;&#x662F;&#xFF0C;&#x8FD9;&#x4E2A;&#x7ED8;&#x5236;&#x8FB9;&#x754C;&#x9700;&#x8981;&#x7531;&#x5F00;&#x53D1;&#x8005;&#x901A;&#x8FC7;<code>RepaintBoundary</code> &#x7EC4;&#x4EF6;&#x81EA;&#x5DF1;&#x6307;&#x5B9A;&#xFF0C;&#x5982;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token function">CustomPaint</span><span class="token punctuation">(</span>
  size<span class="token punctuation">:</span> <span class="token function">Size</span><span class="token punctuation">(</span><span class="token number">300</span><span class="token punctuation">,</span> <span class="token number">300</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token comment">//&#x6307;&#x5B9A;&#x753B;&#x5E03;&#x5927;&#x5C0F;</span>
  painter<span class="token punctuation">:</span> <span class="token function">MyPainter</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
  child<span class="token punctuation">:</span> <span class="token function">RepaintBoundary</span><span class="token punctuation">(</span>
    child<span class="token punctuation">:</span> <span class="token function">Container</span><span class="token punctuation">(</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
  <span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token punctuation">)</span><span class="token punctuation">,</span>
</code></pre>
<p>&#x4E0B;&#x9762;&#x6211;&#x4EEC;&#x770B;&#x770B;<code>RepaintBoundary</code>&#x7684;&#x539F;&#x7406;&#xFF0C;<code>RenderObject</code>&#x6709;&#x4E00;&#x4E2A;<code>isRepaintBoundary</code>&#x5C5E;&#x6027;&#xFF0C;&#x8BE5;&#x5C5E;&#x6027;&#x51B3;&#x5B9A;&#x8FD9;&#x4E2A;<code>RenderObject</code>&#x91CD;&#x7ED8;&#x65F6;&#x662F;&#x5426;&#x72EC;&#x7ACB;&#x4E8E;&#x5176;&#x7236;&#x5143;&#x7D20;&#xFF0C;&#x5982;&#x679C;&#x8BE5;&#x5C5E;&#x6027;&#x503C;&#x4E3A;<code>true</code> &#xFF0C;&#x5219;&#x72EC;&#x7ACB;&#x7ED8;&#x5236;&#xFF0C;&#x53CD;&#x4E4B;&#x5219;&#x4E00;&#x8D77;&#x7ED8;&#x5236;&#x3002;&#x90A3;&#x72EC;&#x7ACB;&#x7ED8;&#x5236;&#x662F;&#x600E;&#x4E48;&#x5B9E;&#x73B0;&#x7684;&#x5462;&#xFF1F; &#x7B54;&#x6848;&#x5C31;&#x5728;<code>paintChild()</code>&#x6E90;&#x7801;&#x4E2D;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">void</span> <span class="token function">paintChild</span><span class="token punctuation">(</span>RenderObject child<span class="token punctuation">,</span> Offset offset<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>child<span class="token punctuation">.</span>isRepaintBoundary<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token function">stopRecordingIfNeeded</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">_compositeChild</span><span class="token punctuation">(</span>child<span class="token punctuation">,</span> offset<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    child<span class="token punctuation">.</span><span class="token function">_paintWithContext</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">,</span> offset<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x770B;&#x5230;&#xFF0C;&#x5728;&#x7ED8;&#x5236;&#x5B50;&#x8282;&#x70B9;&#x65F6;&#xFF0C;&#x5982;&#x679C;<code>child.isRepaintBoundary</code> &#x4E3A; <code>true</code>&#x5219;&#x4F1A;&#x8C03;&#x7528;<code>_compositeChild()</code>&#x65B9;&#x6CD5;&#xFF0C;<code>_compositeChild()</code>&#x6E90;&#x7801;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">void</span> <span class="token function">_compositeChild</span><span class="token punctuation">(</span>RenderObject child<span class="token punctuation">,</span> Offset offset<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token comment">// &#x7ED9;&#x5B50;&#x8282;&#x70B9;&#x521B;&#x5EFA;&#x4E00;&#x4E2A;layer &#xFF0C;&#x7136;&#x540E;&#x518D;&#x4E0A;&#x9762;&#x7ED8;&#x5236;&#x5B50;&#x8282;&#x70B9; </span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>child<span class="token punctuation">.</span>_needsPaint<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token function">repaintCompositedChild</span><span class="token punctuation">(</span>child<span class="token punctuation">,</span> debugAlsoPaintedParent<span class="token punctuation">:</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">assert</span><span class="token punctuation">(</span>child<span class="token punctuation">.</span>_layer <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  child<span class="token punctuation">.</span>_layer<span class="token punctuation">.</span>offset <span class="token operator">=</span> offset<span class="token punctuation">;</span>
  <span class="token function">appendLayer</span><span class="token punctuation">(</span>child<span class="token punctuation">.</span>_layer<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x5F88;&#x660E;&#x663E;&#x4E86;&#xFF0C;&#x72EC;&#x7ACB;&#x7ED8;&#x5236;&#x662F;&#x901A;&#x8FC7;&#x5728;&#x4E0D;&#x540C;&#x7684;layer&#xFF08;&#x5C42;&#xFF09;&#x4E0A;&#x7ED8;&#x5236;&#x7684;&#x3002;&#x6240;&#x4EE5;&#xFF0C;&#x5F88;&#x660E;&#x663E;&#xFF0C;&#x6B63;&#x786E;&#x4F7F;&#x7528;<code>isRepaintBoundary</code>&#x5C5E;&#x6027;&#x53EF;&#x4EE5;&#x63D0;&#x9AD8;&#x7ED8;&#x5236;&#x6548;&#x7387;&#xFF0C;&#x907F;&#x514D;&#x4E0D;&#x5FC5;&#x8981;&#x7684;&#x91CD;&#x7ED8;&#x3002;&#x5177;&#x4F53;&#x539F;&#x7406;&#x662F;&#xFF1A;&#x548C;&#x89E6;&#x53D1;&#x91CD;&#x65B0;build&#x548C;layout&#x7C7B;&#x4F3C;&#xFF0C;<code>RenderObject</code>&#x4E5F;&#x63D0;&#x4F9B;&#x4E86;&#x4E00;&#x4E2A;<code>markNeedsPaint()</code>&#x65B9;&#x6CD5;&#xFF0C;&#x5176;&#x6E90;&#x7801;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">void</span> <span class="token function">markNeedsPaint</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
 <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
  <span class="token comment">//&#x5982;&#x679C;RenderObject.isRepaintBoundary &#x4E3A;true,&#x5219;&#x8BE5;RenderObject&#x62E5;&#x6709;layer&#xFF0C;&#x76F4;&#x63A5;&#x7ED8;&#x5236;  </span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>isRepaintBoundary<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>owner <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token comment">//&#x627E;&#x5230;&#x6700;&#x8FD1;&#x7684;layer&#xFF0C;&#x7ED8;&#x5236;  </span>
      owner<span class="token punctuation">.</span>_nodesNeedingPaint<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      owner<span class="token punctuation">.</span><span class="token function">requestVisualUpdate</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>parent <span class="token operator">is</span> RenderObject<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token comment">// &#x6CA1;&#x6709;&#x81EA;&#x5DF1;&#x7684;layer, &#x4F1A;&#x548C;&#x4E00;&#x4E2A;&#x7956;&#x5148;&#x8282;&#x70B9;&#x5171;&#x7528;&#x4E00;&#x4E2A;layer  </span>
    <span class="token keyword">assert</span><span class="token punctuation">(</span>_layer <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">final</span> RenderObject parent <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>parent<span class="token punctuation">;</span>
    <span class="token comment">// &#x5411;&#x7236;&#x7EA7;&#x9012;&#x5F52;&#x67E5;&#x627E;  </span>
    parent<span class="token punctuation">.</span><span class="token function">markNeedsPaint</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">assert</span><span class="token punctuation">(</span>parent <span class="token operator">==</span> <span class="token keyword">this</span><span class="token punctuation">.</span>parent<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token comment">// &#x5982;&#x679C;&#x76F4;&#x5230;&#x6839;&#x8282;&#x70B9;&#x4E5F;&#x6CA1;&#x627E;&#x5230;&#x4E00;&#x4E2A;Layer&#xFF0C;&#x90A3;&#x4E48;&#x4FBF;&#x9700;&#x8981;&#x7ED8;&#x5236;&#x81EA;&#x8EAB;&#xFF0C;&#x56E0;&#x4E3A;&#x6CA1;&#x6709;&#x5176;&#x5B83;&#x8282;&#x70B9;&#x53EF;&#x4EE5;&#x7ED8;&#x5236;&#x6839;&#x8282;&#x70B9;&#x3002;  </span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>owner <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
      owner<span class="token punctuation">.</span><span class="token function">requestVisualUpdate</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x53EF;&#x4EE5;&#x770B;&#x51FA;&#xFF0C;&#x5F53;&#x8C03;&#x7528; <code>markNeedsPaint()</code> &#x65B9;&#x6CD5;&#x65F6;&#xFF0C;&#x4F1A;&#x4ECE;&#x5F53;&#x524D; <code>RenderObject</code> &#x5F00;&#x59CB;&#x4E00;&#x76F4;&#x5411;&#x7236;&#x8282;&#x70B9;&#x67E5;&#x627E;&#xFF0C;&#x76F4;&#x5230;&#x627E;&#x5230; &#x4E00;&#x4E2A;<code>isRepaintBoundary</code> &#x4E3A; <code>true</code>&#x7684;<code>RenderObject</code> &#x65F6;&#xFF0C;&#x624D;&#x4F1A;&#x89E6;&#x53D1;&#x91CD;&#x7ED8;&#xFF0C;&#x8FD9;&#x6837;&#x4FBF;&#x53EF;&#x4EE5;&#x5B9E;&#x73B0;&#x5C40;&#x90E8;&#x91CD;&#x7ED8;&#x3002;&#x5F53; &#x6709;<code>RenderObject</code> &#x7ED8;&#x5236;&#x7684;&#x5F88;&#x9891;&#x7E41;&#x6216;&#x5F88;&#x590D;&#x6742;&#x65F6;&#xFF0C;&#x53EF;&#x4EE5;&#x901A;&#x8FC7;RepaintBoundary Widget&#x6765;&#x6307;&#x5B9A;<code>isRepaintBoundary</code> &#x4E3A; <code>true</code>&#xFF0C;&#x8FD9;&#x6837;&#x5728;&#x7ED8;&#x5236;&#x65F6;&#x4EC5;&#x4F1A;&#x91CD;&#x7ED8;&#x81EA;&#x8EAB;&#x800C;&#x65E0;&#x9700;&#x91CD;&#x7ED8;&#x5B83;&#x7684; parent&#xFF0C;&#x5982;&#x6B64;&#x4FBF;&#x53EF;&#x63D0;&#x9AD8;&#x6027;&#x80FD;&#x3002;</p>
<p>&#x8FD8;&#x6709;&#x4E00;&#x4E2A;&#x95EE;&#x9898;&#xFF0C;&#x901A;&#x8FC7;<code>RepaintBoundary</code> &#x5982;&#x4F55;&#x8BBE;&#x7F6E;<code>isRepaintBoundary</code>&#x5C5E;&#x6027;&#x5462;&#xFF1F;&#x5176;&#x5B9E;&#xFF0C;&#x5982;&#x679C;&#x4F7F;&#x7528;&#x4E86;<code>RepaintBoundary</code>&#xFF0C;&#x5176;&#x5BF9;&#x5E94;&#x7684;<code>RenderRepaintBoundary</code>&#x4F1A;&#x81EA;&#x52A8;&#x5C06;<code>isRepaintBoundary</code>&#x8BBE;&#x4E3A;<code>true</code>&#x7684;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">class</span> <span class="token class-name">RenderRepaintBoundary</span> <span class="token keyword">extends</span> <span class="token class-name">RenderProxyBox</span> <span class="token punctuation">{</span>
  <span class="token comment">/// Creates a repaint boundary around [child].</span>
  <span class="token function">RenderRepaintBoundary</span><span class="token punctuation">(</span><span class="token punctuation">{</span> RenderBox child <span class="token punctuation">}</span><span class="token punctuation">)</span> <span class="token punctuation">:</span> <span class="token keyword">super</span><span class="token punctuation">(</span>child<span class="token punctuation">)</span><span class="token punctuation">;</span>

  <span class="token metadata symbol">@override</span>
  bool <span class="token keyword">get</span> isRepaintBoundary <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<h2 id="1433-&#x547D;&#x4E2D;&#x6D4B;&#x8BD5;">14.3.3 &#x547D;&#x4E2D;&#x6D4B;&#x8BD5;</h2>
<p>&#x6211;&#x4EEC;&#x5728;&#x201C;&#x4E8B;&#x4EF6;&#x5904;&#x7406;&#x4E0E;&#x901A;&#x77E5;&#x201D;&#x4E00;&#x7AE0;&#x4E2D;&#x5DF2;&#x7ECF;&#x8BB2;&#x8FC7;Flutter&#x4E8B;&#x4EF6;&#x673A;&#x5236;&#x548C;&#x547D;&#x4E2D;&#x6D4B;&#x8BD5;&#x6D41;&#x7A0B;&#xFF0C;&#x672C;&#x8282;&#x6211;&#x4EEC;&#x770B;&#x4E00;&#x4E0B;&#x5176;&#x5185;&#x90E8;&#x5B9E;&#x73B0;&#x539F;&#x7406;&#x3002;</p>
<p>&#x4E00;&#x4E2A;&#x5BF9;&#x8C61;&#x662F;&#x5426;&#x53EF;&#x4EE5;&#x54CD;&#x5E94;&#x4E8B;&#x4EF6;&#xFF0C;&#x53D6;&#x51B3;&#x4E8E;&#x5176;&#x5BF9;&#x547D;&#x4E2D;&#x6D4B;&#x8BD5;&#x7684;&#x8FD4;&#x56DE;&#xFF0C;&#x5F53;&#x53D1;&#x751F;&#x7528;&#x6237;&#x4E8B;&#x4EF6;&#x65F6;&#xFF0C;&#x4F1A;&#x4ECE;&#x6839;&#x8282;&#x70B9;&#xFF08;<code>RenderView</code>&#xFF09;&#x5F00;&#x59CB;&#x8FDB;&#x884C;&#x547D;&#x4E2D;&#x6D4B;&#x8BD5;&#xFF0C;&#x4E0B;&#x9762;&#x662F;<code>RenderView</code>&#x7684;<code>hitTest()</code>&#x6E90;&#x7801;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart">bool <span class="token function">hitTest</span><span class="token punctuation">(</span>HitTestResult result<span class="token punctuation">,</span> <span class="token punctuation">{</span> Offset position <span class="token punctuation">}</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>child <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
    child<span class="token punctuation">.</span><span class="token function">hitTest</span><span class="token punctuation">(</span>result<span class="token punctuation">,</span> position<span class="token punctuation">:</span> position<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//&#x9012;&#x5F52;&#x5B50;RenderBox&#x8FDB;&#x884C;&#x547D;&#x4E2D;&#x6D4B;&#x8BD5;</span>
  result<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token function">HitTestEntry</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//&#x5C06;&#x6D4B;&#x8BD5;&#x7ED3;&#x679C;&#x6DFB;&#x52A0;&#x5230;result&#x4E2D;</span>
  <span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x6211;&#x4EEC;&#x518D;&#x770B;&#x770B;<code>RenderBox</code>&#x9ED8;&#x8BA4;&#x7684;<code>hitTest()</code>&#x5B9E;&#x73B0;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart">bool <span class="token function">hitTest</span><span class="token punctuation">(</span>HitTestResult result<span class="token punctuation">,</span> <span class="token punctuation">{</span> <span class="token metadata symbol">@required</span> Offset position <span class="token punctuation">}</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>  
  <span class="token keyword">if</span> <span class="token punctuation">(</span>_size<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span>position<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">hitTestChildren</span><span class="token punctuation">(</span>result<span class="token punctuation">,</span> position<span class="token punctuation">:</span> position<span class="token punctuation">)</span> <span class="token operator">||</span> <span class="token function">hitTestSelf</span><span class="token punctuation">(</span>position<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      result<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token function">BoxHitTestEntry</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">,</span> position<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      <span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x6211;&#x4EEC;&#x770B;&#x5230;&#x9ED8;&#x8BA4;&#x7684;&#x5B9E;&#x73B0;&#x91CC;&#x8C03;&#x7528;&#x4E86;<code>hitTestSelf()</code>&#x548C;<code>hitTestChildren()</code>&#x4E24;&#x4E2A;&#x65B9;&#x6CD5;&#xFF0C;&#x8FD9;&#x4E24;&#x4E2A;&#x65B9;&#x6CD5;&#x9ED8;&#x8BA4;&#x5B9E;&#x73B0;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart">
<span class="token metadata symbol">@protected</span>
bool <span class="token function">hitTestSelf</span><span class="token punctuation">(</span>Offset position<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token boolean">false</span><span class="token punctuation">;</span>

<span class="token metadata symbol">@protected</span>
bool <span class="token function">hitTestChildren</span><span class="token punctuation">(</span>HitTestResult result<span class="token punctuation">,</span> <span class="token punctuation">{</span> Offset position <span class="token punctuation">}</span><span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
</code></pre>
<p><code>hitTest</code> &#x65B9;&#x6CD5;&#x7528;&#x6765;&#x5224;&#x65AD;&#x8BE5;<code>RenderObject</code> &#x662F;&#x5426;&#x5728;&#x88AB;&#x70B9;&#x51FB;&#x7684;&#x8303;&#x56F4;&#x5185;&#xFF0C;&#x540C;&#x65F6;&#x8D1F;&#x8D23;&#x5C06;&#x88AB;&#x70B9;&#x51FB;&#x7684; <code>RenderBox</code> &#x6DFB;&#x52A0;&#x5230; <code>HitTestResult</code> &#x5217;&#x8868;&#x4E2D;&#xFF0C;&#x53C2;&#x6570; <code>position</code> &#x4E3A;&#x4E8B;&#x4EF6;&#x89E6;&#x53D1;&#x7684;&#x5750;&#x6807;&#xFF08;&#x5982;&#x679C;&#x6709;&#x7684;&#x8BDD;&#xFF09;&#xFF0C;&#x8FD4;&#x56DE; true &#x5219;&#x8868;&#x793A;&#x6709;<code>RenderBox</code> &#x901A;&#x8FC7;&#x4E86;&#x547D;&#x4E2D;&#x6D4B;&#x8BD5;&#xFF0C;&#x9700;&#x8981;&#x54CD;&#x5E94;&#x4E8B;&#x4EF6;&#xFF0C;&#x53CD;&#x4E4B;&#x5219;&#x8BA4;&#x4E3A;&#x5F53;&#x524D;<code>RenderBox</code>&#x6CA1;&#x6709;&#x547D;&#x4E2D;&#x3002;&#x5728;&#x7EE7;&#x627F;<code>RenderBox</code>&#x65F6;&#xFF0C;&#x53EF;&#x4EE5;&#x76F4;&#x63A5;&#x91CD;&#x5199;<code>hitTest()</code>&#x65B9;&#x6CD5;&#xFF0C;&#x4E5F;&#x53EF;&#x4EE5;&#x91CD;&#x5199; <code>hitTestSelf()</code> &#x6216; <code>hitTestChildren()</code>, &#x552F;&#x4E00;&#x4E0D;&#x540C;&#x7684;&#x662F; <code>hitTest()</code>&#x4E2D;&#x9700;&#x8981;&#x5C06;&#x901A;&#x8FC7;&#x547D;&#x4E2D;&#x6D4B;&#x8BD5;&#x7684;&#x8282;&#x70B9;&#x4FE1;&#x606F;&#x6DFB;&#x52A0;&#x5230;&#x547D;&#x4E2D;&#x6D4B;&#x8BD5;&#x7ED3;&#x679C;&#x5217;&#x8868;&#x4E2D;&#xFF0C;&#x800C; <code>hitTestSelf()</code> &#x548C; <code>hitTestChildren()</code>&#x5219;&#x53EA;&#x9700;&#x8981;&#x7B80;&#x5355;&#x7684;&#x8FD4;&#x56DE;<code>true</code>&#x6216;<code>false</code>&#x3002;</p>
<h2 id="1434-&#x8BED;&#x4E49;&#x5316;">14.3.4 &#x8BED;&#x4E49;&#x5316;</h2>
<p>&#x8BED;&#x4E49;&#x5316;&#x5373;Semantics&#xFF0C;&#x4E3B;&#x8981;&#x662F;&#x63D0;&#x4F9B;&#x7ED9;&#x8BFB;&#x5C4F;&#x8F6F;&#x4EF6;&#x7684;&#x63A5;&#x53E3;&#xFF0C;&#x4E5F;&#x662F;&#x5B9E;&#x73B0;&#x8F85;&#x52A9;&#x529F;&#x80FD;&#x7684;&#x57FA;&#x7840;&#xFF0C;&#x901A;&#x8FC7;&#x8BED;&#x4E49;&#x5316;&#x63A5;&#x53E3;&#x53EF;&#x4EE5;&#x8BA9;&#x673A;&#x5668;&#x7406;&#x89E3;&#x9875;&#x9762;&#x4E0A;&#x7684;&#x5185;&#x5BB9;&#xFF0C;&#x5BF9;&#x4E8E;&#x6709;&#x89C6;&#x529B;&#x969C;&#x788D;&#x7528;&#x6237;&#x53EF;&#x4EE5;&#x4F7F;&#x7528;&#x8BFB;&#x5C4F;&#x8F6F;&#x4EF6;&#x6765;&#x7406;&#x89E3;UI&#x5185;&#x5BB9;&#x3002;&#x5982;&#x679C;&#x4E00;&#x4E2A;<code>RenderObject</code>&#x8981;&#x652F;&#x6301;&#x8BED;&#x4E49;&#x5316;&#x63A5;&#x53E3;&#xFF0C;&#x53EF;&#x4EE5;&#x5B9E;&#x73B0; <code>describeApproximatePaintClip</code>&#x548C; <code>visitChildrenForSemantics</code>&#x65B9;&#x6CD5;&#x548C;<code>semanticsAnnotator</code> getter&#x3002;&#x66F4;&#x591A;&#x5173;&#x4E8E;&#x8BED;&#x4E49;&#x5316;&#x7684;&#x4FE1;&#x606F;&#x53EF;&#x4EE5;&#x67E5;&#x770B;API&#x6587;&#x6863;&#x3002;</p>
<h2 id="1435-&#x603B;&#x7ED3;">14.3.5 &#x603B;&#x7ED3;</h2>
<p>&#x672C;&#x8282;&#x6211;&#x4EEC;&#x4ECB;&#x7ECD;&#x4E86;<code>RenderObject</code>&#x4E3B;&#x8981;&#x7684;&#x529F;&#x80FD;&#x548C;&#x65B9;&#x6CD5;&#xFF0C;&#x7406;&#x89E3;&#x8FD9;&#x4E9B;&#x5185;&#x5BB9;&#x53EF;&#x4EE5;&#x5E2E;&#x52A9;&#x6211;&#x4EEC;&#x66F4;&#x597D;&#x7684;&#x7406;&#x89E3;Flutter UI&#x5E95;&#x5C42;&#x539F;&#x7406;&#x3002;&#x6211;&#x4EEC;&#x4E5F;&#x53EF;&#x4EE5;&#x770B;&#x5230;&#xFF0C;&#x5982;&#x679C;&#x8981;&#x4ECE;&#x5934;&#x5230;&#x5C3E;&#x5B9E;&#x73B0;&#x4E00;&#x4E2A;<code>RenderObject</code>&#x662F;&#x6BD4;&#x8F83;&#x9EBB;&#x70E6;&#x7684;&#xFF0C;&#x6211;&#x4EEC;&#x5FC5;&#x987B;&#x53BB;&#x5B9E;&#x73B0;layout&#x3001;&#x7ED8;&#x5236;&#x548C;&#x547D;&#x4E2D;&#x6D4B;&#x8BD5;&#x903B;&#x8F91;&#xFF0C;&#x4F46;&#x662F;&#x503C;&#x5F97;&#x5E86;&#x5E78;&#x7684;&#x662F;&#xFF0C;&#x5927;&#x591A;&#x6570;&#x65F6;&#x5019;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x76F4;&#x63A5;&#x5728;Widget&#x5C42;&#x901A;&#x8FC7;&#x7EC4;&#x5408;&#x6216;&#x8005;<code>CustomPaint</code>&#x5B8C;&#x6210;&#x81EA;&#x5B9A;&#x4E49;UI&#x3002;&#x5982;&#x679C;&#x9047;&#x5230;&#x53EA;&#x80FD;&#x5B9A;&#x4E49;&#x4E00;&#x4E2A;&#x65B0;<code>RenderObject</code>&#x7684;&#x573A;&#x666F;&#x65F6;&#xFF08;&#x5982;&#x8981;&#x5B9E;&#x73B0;&#x4E00;&#x4E2A;&#x65B0;&#x7684;layout&#x7B97;&#x6CD5;&#x7684;&#x5E03;&#x5C40;&#x5BB9;&#x5668;&#xFF09;&#xFF0C;&#x53EF;&#x4EE5;&#x76F4;&#x63A5;&#x7EE7;&#x627F;&#x81EA;<code>RenderBox</code>&#xFF0C;&#x8FD9;&#x6837;&#x53EF;&#x4EE5;&#x5E2E;&#x6211;&#x4EEC;&#x51CF;&#x5C11;&#x4E00;&#x90E8;&#x5206;&#x5DE5;&#x4F5C;&#x3002;</p>

                                
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